#include<iostream>
using namespace std;
int main()
{
    float money = 0;
    cin>>money;
    float Mode1 = money-10;
    float Mode2 = money*0.9;
    cout.flags(ios::fixed);
    cout.precision(2);
    if(money>50.0f&&Mode1<Mode2)
    {
        cout<<Mode1<<endl;
    }
    else cout<<Mode2<<endl;

}